Pathways to lexical ambiguity: fMRI evidence for bilateral fronto-parietal involvement in language processing (original) (raw)
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Brain and Language, 2002
Nine individuals with complex language deficits following left-hemisphere cortical lesions and a matched control group (n ϭ 9) performed speeded lexical decisions on the third word of auditory word triplets containing a lexical ambiguity. The critical conditions were concordant (e.g., coin-bank-money), discordant (e.g., river-bank-money), neutral (e.g., day-bankmoney), and unrelated (e.g., river-day-money). Triplets were presented with an interstimulus interval (ISI) of 100 and 1250 ms. Overall, the left-hemisphere-damaged subjects appeared able to exhaustively access meanings for lexical ambiguities rapidly, but were unable to reduce the level of activation for contextually inappropriate meanings at both short and long ISIs, unlike control subjects. These findings are consistent with a disruption of the proposed role of the left hemisphere in selecting and suppressing meanings via contextual integration and a sparing of the right-hemisphere mechanisms responsible for maintaining alternative meanings.
Task-Dependent Modulation of Regions in the Left Inferior Frontal Cortex during Semantic Processing
Journal of Cognitive Neuroscience, 2001
& To distinguish areas involved in the processing of word meaning (semantics) from other regions involved in lexical processing more generally, subjects were scanned with positron emission tomography (PET) while performing lexical tasks, three of which required varying degrees of semantic analysis and one that required phonological analysis. Three closely apposed regions in the left inferior frontal cortex and one in the right cerebellum were significantly active above baseline in the semantic tasks, but not in the nonsemantic task. The activity in two of the frontal regions was modulated by the difficulty of the semantic judgment. Other regions, including some in the left temporal cortex and the cerebellum, were active across all four language tasks. Thus, in addition to a number of regions known to be active during language processing, regions in the left inferior frontal cortex were specifically recruited during semantic processing in a task-dependent manner. A region in the right cerebellum may be functionally related to those in the left inferior frontal cortex. Discussion focuses on the implications of these results for current views regarding neural substrates of semantic processing. & D
Semantic ambiguity processing in sentence context: Evidence from event-related fMRI
NeuroImage, 2007
Lexical semantic ambiguity is the phenomenon when a word has multiple meanings (e.g. 'bank'). The aim of this event-related functional MRI study was to identify those brain areas, which are involved in contextually driven ambiguity resolution. Ambiguous words were selected which have a most frequent, dominant, and less frequent, subordinate meaning. These words were presented in two types of sentences: (1) a sentence congruent with the dominant interpretation and (2) a sentence congruent with the subordinate interpretation. Sentences without ambiguous words served as a control condition. The ambiguous words always occurred early in the sentences and were biased towards one particular meaning by the final word(s) of the sentence; the event at the end of the sentences was modeled. The results indicate that a bilaterally distributed network supports semantic ambiguity comprehension: left (BA 45/44) and right (BA 47) inferior frontal gyri and left (BA 20/37) and right inferior/ middle temporal gyri (BA 20). The pattern of activation is most consistent with a scenario in which initially a frequency-based probabilistic choice is made between the alternative meanings, and the meaning is updated when this interpretation does not fit into the final disambiguating context. The neural pattern is consistent with the results of other neuroimaging experiments which manipulated various aspects of integrative and context processing task demands. The presence of a bilateral network is also in line with the lesion and divided visual field literature, but contrary to earlier claims, the two hemispheres appear to play similar roles during semantic ambiguity resolution.
Variability of fMRI activation during a phonological and semantic language task in healthy subjects
Human Brain Mapping, 2004
Assessing inter-individual variability of functional activations is of practical importance in the use of functional magnetic resonance imaging (fMRI) in a clinical context. In this fMRI study we addressed this issue in 30 right-handed, healthy subjects using rhyme detection (phonologic) and semantic categorization tasks. Significant activations, found mainly in the left hemisphere, concerned the inferior frontal gyrus, the superior/middle temporal gyri, the prefrontal cortex, the inferior parietal lobe, the superior parietal lobule/superior occipital gyrus, the pre-central gyrus, and the supplementary motor area. Intensity/spatial analysis comparing activations in both tasks revealed an increased involvement of frontal regions in the semantic task and of temporo-parietal regions in the phonologic task. The frequency of activation analyzed in nine regional subdivisions revealed a high inter-subject variability but showed that the most frequently activated regions were the inferior frontal gyrus and the prefrontal cortex. Laterality indices, strongly lateralizing in both tasks, were slightly higher in the semantic (0.76 Ϯ 0.19) than the phonologic task (0.66 Ϯ 0.27). Frontal dominance indices (a measure of frontal vs. posterior left hemisphere dominance) indicated more robust frontal activations in the semantic than the phonologic task. Our study allowed the characterization of the most frequently involved foci in two language tasks and showed that the combination of these tasks constitutes a suitable tool for determining language lateralization and for mapping major language areas. Hum Brain Mapp 23: 140 -155, 2004.
Brain and Behavior, 2013
This study examined the effects of linguistic task demands on the neuroanatomical localization of the neural response related to automatic semantic processing of concrete German nouns combining the associative priming paradigm with functional magnetic resonance imaging (fMRI). To clarify the functional role of the inferior frontal gyrus (IFG) for semantic processing with respect to semantic decision making compared to semantic processing per se, we used a linguistic task that involved either a binary decision process (i.e., semantic categorization; Experiment 1) or not (i.e., silently thinking about a word's meaning; Experiment 2). We observed associative priming effects indicated as neural suppression in bilateral superior temporal gyri (STG), anterior cingulate cortex (ACC), occipitotemporal brain areas, and in medial frontal brain areas independently of the linguistic task. Inferior parietal brain areas were more active for silently thinking about a word's meaning compared to semantic categorization. A conjunction analysis of linguistic task revealed that both tasks activated the same leftlateralized occipito-temporo-frontal network including the IFG. Contrasting neural associative priming effects across linguistic task demands, we found a significant interaction in the right IFG. The present fMRI data give rise to the assumption that activation of the left inferior frontal gyrus (LIFG) in the semantic domain might be important for semantic processing in general and not only for semantic decision making. These findings contrast with a recent study regarding the role of the LIFG for binary decision making in the lexical domain (Wright et al. 2011).
Journal of clinical …, 2006
To determine whether frontal lobe regions, including BrocaÕs area, dorsolateral prefrontal cortex (DLPFC) and supplementary motor area (SMA), are differentially activated during lexical and semantic language tasks, we used functional magnetic resonance imaging in eight healthy right-handed subjects silently performing two semantic tasks (adjective and verb generation) and a lexical retrieval task (noun recall). Activation was observed in BrocaÕs area, DLPFC and SMA for all tasks. BrocaÕs area activation was approximately doubled during the semantic tasks compared with the lexical task (verbs vs nouns: 19.1 ± 4.5 vs 8.9 ± 1.6 voxels, p = 0.02; adjectives vs nouns 24.4 ± 7.5 vs 10.1 ± 2.8 voxels, p = 0.04); however, there were no significant differences in the DLFPC or SMA across tasks. We conclude that BrocaÕs area is more active during tasks that have a semantic content, whereas areas involved in preparatory processing (SMA) and memory retrieval (DLPFC) are engaged equally during both types of task.
Linguistic theory and neuroimaging evidence: an fMRI study of Broca’s area in lexical semantics
Neuropsychologia, 2003
There has been a long debate on the functional characterization of left inferior frontal cortex, including proposals regarding syntactic and lexico-semantic involvement. We studied nine right-handed adults, using functional magnetic resonance imaging (fMRI) during performance on a semantic decision task in which subjects had to determine whether noun-verb pairs were semantically associated. In comparison with a visuoperceptual control task, activation clusters were seen in left inferior frontal and middle temporal regions, as well as the bilateral superior frontal gyrus. In agreement with previous studies, our findings suggest that Broca's area is involved in semantic processing. Findings of lexico-semantic as well as syntactic processing in the inferior frontal lobe may be accounted for in terms of working memory demands.
Engagement of right temporal cortex during processing of linguistic context
Neuropsychologia, 2001
Language processing involves the interplay of areas in both cerebral hemispheres. Whereas the left temporal lobe is necessary for most language tasks, the right hemisphere seems to be additionally activated during processing of paragraphs and metaphors. We studied the neural correlates of word generation and selection in a sentence context, using functional magnetic resonance imaging (fMRI). Cerebral activation was measured while seven healthy, right handed volunteers read and completed sentence stems, with relatively low Cloze frequency, out loud. During a GENERATION condition, subjects were required to generate a word which completed a sentence stem appropriately. During a DECISION condition, subjects selected and articulated one of two presented terminal words. A READING condition in which subjects read an appropriate completion aloud, served as baseline. When GENERATION was compared to READING or DECISION, the left middle frontal, anterior cingulate, precuneus and right lateral temporal cortex were activated. During DECISION relative to READING, the left inferior frontal and middle/superior temporal cortex bilaterally were activated. The prominent engagement of the right lateral temporal cortex during the GENERATION conditions may reflect the processing of linguistic context, and particularly the activation of multiple meanings in the course of producing an appropriate completion.